Time-limit device



Sept. 1, 1925. 5 1,552,375

C. D. AINSWORTH TIME LIMIT DEVI CE Filed Jan. 8, 1921 fizz/671202: (fi u Patented Sept. 1 1925.

UNITED. STATES P. t'llE1N'I OFFICE.

CHESTER D. AI'NSWORTH, OF WOLLASTON, MASSACHUSETTS, ASSIGNOR, BY v ASSIGNMENTS, T0 CONDIT ELECTRICAL MANUFACTURING COMPANY, A CORPORA- TION OF MASSACHUSETTS.

TIME-LIMIT DEVICE.

Application filed January 8, 1921. Serial No. 435,957.

To all whom it may concern:

Be it known that I, CHESTER D. Ants- WORTH, a citizen of the United. States, residing at Wollaston, in the county of Norfolk and State of Massachusetts, have invented an Improvement in Time-Limit Devices, of

which the following is a specification.

This invention relates to time limit relays of the type comprising a solenoid wound upon a tube which formsthe cylinder of a dash pot. A piston is movably disposed within said tube and has-a magnetic core by which it is moved. 7 I

The device may be, and preferably is, 1mmersed in oil. Oil or other fluid is adapted ,-to be entrapped between the closed end of the cylinder and the piston and the rate of flow of oil or other fluid from the cylinder under pressure determines the operating characteristics of the device.

The object of my invention is to improve the construction and operation of a time limit relay of the type above set forth.

The tube comprising the cylinder of the device and on which the solenoid winding is received has heretofore been made of brass or other electrically conducting material. The internal bore of the tube must be accurately formed in order that the piston, which also must be accurately formed, may fit therein to prevent leakage of oil past the piston and yet 'JlOl; restrict the free movement of the piston; or if the device is designed for oil leakage past the piston, as is common practice, the clearmice or leakage space must be accurately formed in order that the relay may function in accordance with a predetermined operating characteristic. For this purpose, the wall of the metallic tube is made relatively thick in order to prevent distortion of the tube under manufacturing stresses.

In carrying out-my invention, I form' the tube which comprises the cylinder of the dash pot of an electrically insulating, as contrasted with an electrically conducting, material; and I find that marked advantages accrue from the use of such a material.

. I find that the expense of construction of the device is greatly decreased.

I find that I may employ a considerably smaller solenoid winding, which consequently has less copper in it, to provide the same magnetic. pull on the core at a predetermined value of current; or, conversely, for the same number of ampere turns of the solenoid winding, the pull on the core is largely increased.

In some devices of the type to which this invention appertains it is found that, under certain conditions, there is not enou h pull on the core to trip the switch after t e core has been moved upward into tripping position against the resistance of the oil. With a device embodying my invention there appears to be at all times ample power to trip the switch at the end of the extreme move ment of the core.

I find that with my invention the operating characteristics of the device are materially improved. Whereas in that type of device having a brass-tube, the range of calibration was short and the settings of the core for current values were close together, in my new device the calibration scale is relatively very open and the current calibrations are relatively wide apart. This results in a device which may be accurately adjusted positively to operate at any desired current setting as contrasted with the heretofore common construction.

A reason for the marked advantages accruing from theuse of my invention over the common construction would appear to be the absenceof the transformer or inductive eifect of the solenoid winding on the tube, due to the use of an insulating tube for the usual brass tube. The solenoid winding is adapted to be energized from an alternating current source. The solenoid winding and the brass tube constitute elements of a 'transformer'whe'rein the solenoid winding is the primary and the brass tube is the secondary. Due to the low resistance of the brass tube, a heavy current is set up therein; and the current is materially increased by providing the tube with a mechanically necessary thick wall. The generation of current in the secondary results.

in a marked consumption of energy which serves no purpose in attracting the movable core of the device and is in addition to that required to attract the core. Thisconsumption of energy must be compensated for by providing the solenoid winding with an increased number of ampere turns with the result that the expense of the device is correspondingly, and largely, increased. The effect of the brass tube also is greatly to shorten thelength of efiicient tractive effect of the solenoid sothat there is actually only a small length through which the movable core-will be moved. As a consequence, the calibrations are relatively crowded together and the core can not be set accurately at the calibrations; consequently, the device may not respond at the current value for which it was intended to respond. With a tube embodying my invention the calibration scale is open,,as above set forth.

The insulating dash pot forming a feature of-my invention is mechanically strong, has low electrical conductivity, is oil impermeable and admits of being accurately formed into shape. I find that material best adapted for my purposes is a phenol condensation product known as condensite. The phenol condensation product may be accurately molded so that no machine work is necessary with the result that the insulating tube may be made very cheaply although the cheapness of the tube itself is of minor importance when compared with the marked results which accrue from its use. Not all electrically insulating materials are satisfactory for the reason that they are lacking in either one or more of the qualities of strength, electrical resistance, fluid impermeance, or temperature resistance.

Time limit devices of the type above set forth are usually provided with fixed core pieces in the upper end of the tube and cylinder. In my improved construction the fixed core piece is molded in and is an in tegral part of the tube. I It may sometimes happen that the union between the core piece and the material comprising the tube, while mechanically strong, is not fluid tight. To prevent leakage of oil or other fluid from the interior of the tube about the core piece the tube is I formed with a partition or end wall which separates the bore of the tube from the core piece and forms the end wall of said bore. Said end wall is integral with the side wall of the tube whereby the cylinder "is permaw nently sealed at the top and therefore oil leakage can only take place pastthe piston or at some other designated point. W

Fig. 1 is a side elevation of a time limit device embodying my invention immersed in a body of oil.

Fig. 2 is a sectional '.detail of the'movable element of Fig. 1.

Fig. 3 is an enlarged sectional detail of the dash pot cylinder embodying my invention. i

terial preferably, condensite, and molded into shape. The character of the material is such that it takes accurately the dimensions of the mold. and no machine work is necessary. The tube is formed with the internal cylindrical bore 13 extending from the lower end of the tube and which forms the cylinder in which the piston 14 is movably disposed.

Said piston is adjustably threaded on the sleeve 14 to which the core 15 is loosely connected. Said sleeve and core cooperate to form a valve which admits of the rapid recovery of the movable element of the device after an operation, and said piston and sleeve cooperate to provide an adjustable leak passage whereby to vary the time of operationof the device. These features are more elaborately described and are claimed in my co-pending application Serial No. 366,860, filed March 16, 1920.

A striking disc 16 may be secured to the lower end of said core 15 to engage the tripping arm 17 of a switch not shown.

Said piston is a close fit within said cylinder whereby to prevent oil leakage past it and yet is freely. movable therein. The phenol condensation product of which the tube is formed admits of being accurately molded and, consequently, the bore 13 and the piston may fit accurately. Other insulatingmaterials may not'be accurately molded and consequently the fit of the piston within the bore may not be accurate and, consequently, the operating characteristic of the device may not be predetermined.

The side wall of the thick, for mechanical reasons, and also because a considerable magnetic leakage gap between the core and solenoid is conducive to an open calibration scale,-which is a desirable feature. K A core piece 18 is molded in the upper end of the tube and may have recesses or grooves .18 therein in which the material composing the tube is received, whereby it may better be retained m place. Said core piece Ina also be formed with the 19. in which the bolt 20 may be received and by which the device may/be secured to the support 21.

tube is relatively threaded recess While a is possible to utilize the core core 18; The wall is integral with the wall of the tube and effectively seals the upper end of said bore.

. moulded insulating tube having an internal bore, a pole piece imbedded in one end of said tube, said core and tube having complementary interlocking indentations and projections, a solenoid winding disposed on said tube, and a piston operabl within the bore of said tube-an operated by said solenoid winding.

2. A time limi device comprising an insulating tube having an elongated internal bore closed at its upper end, and a magnetic V core fixed in the upper end of the tube above received theclosed end of the bore, a piston movably disposed in said bore, and a solenoid wind-- ing received on said tube. I I

3. A time limit device comprising a tube of molded insulating material having an internal cylindrical bore, an attaching member imbedded in the upper end of said tube, and an end wall integral with the wall of the tube interposed between the attaching member and bore, a piston movably dis posed within said bore and a solenoid winding received on said tube. 4

4. A time limit device comprising a tube of. molded insulating material having an attaching member imbedded in one end of it,

an internal bore, and a sealing wall integral with the wall of the tube interposed between said bore and member, a pistonmovably dis- 4 posed in said bore and a solenoid winding received on said tube.

In testimony whereof, I have signed m name to this specification.

CHESTER D. AINSWORTH. 

